books.google.com - The Encyclopedia of Tracks and Scats is the first comprehensive guidebook for identifying the tracks and scats of all trackable animals of the United States and Canada. With ample use of photographs and line drawings, Len McDougall, an adroit tracker and an experienced teacher of tracking skills, takes...https://books.google.com/books/about/The_Encyclopedia_of_Tracks_and_Scats.html?id=9XOc2_u7z6cC&q=porcupines&utm_source=gb-gplus-shareThe Encyclopedia of Tracks and Scats